It is a key fact about American policy in Vietnam that the withdrawel of American troops was built into it from the start. None of the presidents who waged war in Vietnam contemplated an open-ended campaign; all promised the public that American troops would be able to leave in the not-too-remote future. The promise of withdrawel precluded a policy of occupation of the traditional colonial sort, in which a great power simply imposes its will on a small one indefinitely.

JONATHAN SCHELL, The Real War

It has been said that the United States was deceived into entering and expanding the Vietnam War by its own overoptimistic propaganda. The record suggests, however, that the policy-makers stayed in Vietnam not so much because of overly optimistic hopes of winning ... as because of overly pessimistic assessments of the consequences of losing.